Bearing assembly with surface layer

ABSTRACT

A bearing assembly is disclosed that includes a first component with a first bearing surface, and a second component with a second bearing surface. A fluid is disposed between the first bearing surface and the second bearing surface supporting the first bearing surface and the second bearing surface in a non-contact rotational relationship. The first bearing surface, or the second bearing surface, or both the first bearing surface and the second bearing surface include a surface layer with solid lubricant 2D nanoparticles in a matrix.

BACKGROUND

Bearing assemblies are widely used to provide engagement between amoving component or assembly (i.e., a rotor) and a support or otherstructure that is stationary or that moves at a different speed than themoving component or assembly. One challenge faced by bearing assembliesis management of friction between the moving and non-moving componentsor between components moving at different speeds. Many bearingassemblies utilize one or more rolling surfaces such as balls or otherrollers disposed in a raceway formed by race structures integrated withor attached to the rotor and the support. Other bearing assemblies relyon low-friction sliding surfaces for engagement between the rotor andsupport. Another type of bearing assembly relies on the presence of afluid between the bearing surfaces to maintain the bearing surfaces in anon-contact relationship. The fluid can be a liquid or a gas, with thegas often provided under pressure sufficient to maintain the bearingsurfaces in a non-contact relationship. In many cases, the fluid betweenthe bearing surfaces is pressurized air, and such bearings are commonlyreferred to as “air bearings”.

Non-contact bearing assemblies such as air bearings can provideeffective management of significant frictional forces to the bearingsurfaces. However, friction on the bearing surfaces is not necessarilyeliminated for all operational conditions. For example, in the case ofpressurized air supplied to an aerostatic or hydrostatic bearing, anyinterruption of the pressurized fluid source can subject the bearingsurfaces to frictional contact. Also, non-standard operating conditionssuch as an overload on the bearing assembly can overwhelm the fluidbuffer and force the components into frictional contact. In the case ofaerodynamic or hydrodynamic bearings that rely on the motion of thebearing components themselves or on connected components to generate orpressurize the fluid buffer, the bearing surfaces can come intofrictional contact during commencement or termination of the components'motion (i.e., startup or shutdown).

BRIEF DESCRIPTION

In some embodiments of this disclosure, a bearing assembly comprises afirst component comprising a first bearing surface, and a secondcomponent comprising a second bearing surface. A fluid is disposedbetween the first bearing surface and the second bearing surfacesupporting the first bearing surface and the second bearing surface in anon-contact rotational relationship. The first bearing surface, or thesecond bearing surface, or both the first bearing surface and the secondbearing surface include a surface layer comprising solid lubricant 2Dnanoparticles in a matrix.

In some embodiments, a bearing comprises a support, a bump foil over thesupport, a top foil over the bump foil, and a surface layer over thebump foil comprising solid lubricant 2D nanoparticles in a matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter of this disclosure is particularly pointed out anddistinctly claimed in the claims at the conclusion of the specification.The foregoing and other features, and advantages of the presentdisclosure are apparent from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a partial cross-sectional view of an example embodiment of ajournal bearing;

FIG. 2 is a partial exploded view of an example embodiment thrustbearing; and

FIG. 3 is a schematic cross-sectional view of an air cycle machine.

DETAILED DESCRIPTION

With reference now to the Figures, FIG. 1 is a cross-sectional view ofan example embodiment of a fluid film journal bearing assembly (journalbearing 100). The journal bearing 100 includes a journal sleeve 102 thatdefines an outer diameter surface 104 and an inner diameter surface 106.The journal sleeve 102 is substantially cylindrical and is arrangedabout a central axis. It should be noted that the journal sleeve canhave a conventional cylindrical shape, or can be shaped with aweight-reduced profile, or configured as other shapes or configurations,and FIG. 1 merely presents an exemplary configuration of a journalbearing 100.

In FIG. 1, a number of foils are arranged inside the journal sleeve 102.The journal bearing 100 includes a bump foil 108, an intermediate foil110, and a top foil 122. The bump foil 108, the intermediate foil 110,and the top foil 112 are each formed from thin sheets of material (e.g.,nickel-based alloys, steel, or similar materials) wrapped in a generallycylindrical shape and positioned in a bore of the journal sleeve 102.The bump foil 108 is corrugated, allowing a working fluid and/or coolingfluid to flow through the spaces formed between adjacent corrugations.The bump foil 108 is positioned adjacent to the inner diameter surface106 of the journal sleeve 102. The foils 108, 110, and 112 are retainedrelative to the journal sleeve 102 with bent portions 114 that engage akey slot 116. A rotating component 118, such as a shaft can bepositioned inside the journal bearing 100, radially inward from the topfoil 112. The rotating component 118 is typically in close proximity tothe top foil 112, but for ease of illustration is shown in a partialexploded view with an exaggerated distance between the top foil 112 andthe rotating component 118. During operation, moving air generated byaction of the rotating component 118 urges pressurized air radiallyoutward against the compliant foil structure 108, 110, and 112 to createa fluid air layer separating the rotating component 118 and the journalbearing 100.

As further shown in FIG. 1, a surface layer 120, which is exposed to abearing surface of a rotating component, is disposed over (in this case,radially inward from) the top foil 112. The surface layer 120 comprisessolid lubricant 2D nanoparticles in a matrix. In some embodiments, thesurface layer can have a thickness in a range with a low end of 2 nm, 8,nm, or 12 nm, and a high end of 65 nm, 40 nm, or 20 nm. All possiblecombinations of the above-mentioned range endpoints (excludingimpossible combinations where a low endpoint would have a greater valuethan a high endpoint) are explicitly included herein as disclosedranges. The surface layers discussed herein can be included as a surfacelayer on either or both of the bearing surfaces of relative motion. Forexample, in the case of the example embodiment such as FIG. 1 showing abearing assembly comprising a rotating member 118 and a journal bearing100, the surface layer can be on the surface of the bearing surface onthe radially inner surface of top foil 112 as shown for surface layer120 in FIG. 1, or the surface layer can be on the radially outer surfaceof the rotating member 118, or the surface layer can be on the surfaceof the bearing surface on the radially inner surface of top foil 112 asshown for surface layer 120 in FIG. 1 and on the radially outer surfaceof the rotating member 118.

The matrix of a surface layer such as surface layer 120 can include anysort of matrix material, including but not limited to polymers,ceramics, metal, or matrix materials that can form a continuous phase.In some embodiments, the matrix material comprises a polyamide polymer,a polyimide polymer, or a copolymer comprising polyamide or polyimidesegments. In some embodiments, the matrix material comprises apolyamide-polyimide copolymer. Various application techniques forcreation or application of the surface layer can be utilized by theskilled person. For example, a surface layer can be applied as a polymercoating by spray application of a liquid or powder coating compositioncomprising a polymer matrix material and dispersed solid lubricant 2Dnanoparticles followed by curing to coalesce and solidify the coating.In some embodiments, the solid lubricant 2D nanoparticles are present inthe surface layer at a concentration in a range with a low end of 35 wt.%, 45 wt. %, or 58 wt. %, and a high end of 72 wt. %, 68 wt. %, or 62wt. %, based on the total coating solids. All possible combinations ofthe above-mentioned range endpoints (excluding impossible combinationswhere a low endpoint would have a greater value than a high endpoint)are explicitly included herein as disclosed ranges. The surface layercan also include various other materials. For example, in the case ofpolymer coatings, the surface layer can include various polymer coatingadditives (e.g., curing agents, antioxidants, coating aids, fillers,etc.).

Various materials can be utilized as solid lubricant 2D nanoparticles.As used herein, the term “2D” includes particles with a smallestdimension, or thickness, of 1 to 20 molecular layers, and one or moreanisotropic dimensions along lines or planes that diverge from thethickness. In some embodiments, the anisotropic dimensions can extendbeyond 100 nm, although this is not necessary. In some embodiments, the2D nanoparticles can have an aspect ratio, defined as the ratio of thelargest dimension to the smallest dimension of at least 10. In someembodiments, the 2D nanoparticles can have an aspect ratio, defined asthe ratio of the largest dimension to the smallest dimension of at least100. In some embodiments, the 2D nanoparticles can have an even higheraspect ratio of at least 2500. Higher levels of aspect ratios can beobtained at relatively complete levels of exfoliation, including to thelevel of a single molecular layer. As mentioned above, the 2Dnanoparticles can have a thickness ranging from 1 to 20 molecularlayers. In some embodiments, the 2D nanoparticles can have a thicknessranging from 1 to 15 molecular layers. In some embodiments, the 2Dnanoparticles can have a thickness ranging from 1 to 10 molecularlayers. In some embodiments, the 2D nanoparticles can have a thicknessranging from 1 to 5 molecular layers. In some embodiments, the 2Dnanoparticles can have a thickness ranging from 1 to 4 molecular layers.In some embodiments, the 2D nanoparticles can have a thickness rangingfrom 1 to 3 molecular layers. In some embodiments, the 2D nanoparticlescan have a thickness ranging from 1 to 2 molecular layers. In someembodiments, the 2D nanoparticles can have a thickness of 1 molecularlayer. In some embodiments, the 2D nanoparticles can have a have a meandiameter in a range with a low end of 10 nm, 90 nm, or 1 μm, and a highend of 13 μm, 7 μm, or 5 μm. Mean diameter for 2D nanoparticles can bedetermined using commercially available electron microscopy measurementtools. All possible combinations of the above-mentioned range endpoints(excluding impossible combinations where a low endpoint would have agreater value than a high endpoint) are explicitly included herein asdisclosed ranges. As the term “lubricant” is used herein with respect tothe solid 2D nanoparticles, the solid 2D nanoparticles are considered as“lubricant” nanoparticles if the coating has a coefficient of frictionthat is less than a coefficient of friction of a comparison coating ofthe same matrix material but without the solid 2D nanoparticles.Examples of materials for the solid lubricant 2D nanoparticles includegraphene, hexagonal boron nitride, or molybdenum disulfide. In someembodiments, the surface layer can include lubricant materials inaddition to the solid lubricant 2D nanoparticles. Examples of suchadditional solid lubricant particles or nanoparticles include particlesor nanoparticles of materials such as graphene, hexagonal boron nitride,or hexagonal molybdenum disulfide of different particle sizes than thesolid lubricant 2D nanoparticles.

Solid 2D nanoparticles can be prepared by various techniques. Graphene,for example, can be prepared by different techniques including chemicalvapor deposition onto a substrate up to a target thickness followed byremoval of graphene from the substrate. Solid 2D nanoparticles,including graphene, hexagonal boron nitride, and hexagonal molybdenumdisulfide, can also be prepared by exfoliation of a parent molecularthree-dimensional material such as graphite, unexfoliated hexagonalboron nitride, or unexfoliated hexaganol molybdenum disulfide. Variousexfoliation techniques can be used, including mechanical exfoliation,sonic exfoliation, thermal exfoliation, or chemical exfoliation. Manyexfoliation techniques can be controlled (e.g., by controlling duration,reaction conditions such as agitation speed or temperature, ormaterials, or both duration and reaction conditions or materials) toproduce solid 2D nanoparticles with particle size and configuration in atarget range.

The bearing assembly shown in FIG. 1 is just one of many possibleexample embodiments. Another example embodiment is shown in FIG. 2, inwhich an exploded view is shown of an example embodiment of ahydrodynamic fluid film thrust bearing assembly (“thrust bearing 200”),which represents another type of foil hydrodynamic bearing. As isapparent from the Figures, the thrust bearing 200 of FIG. 2 has adifferent construction than the journal bearing 100 of FIG. 1. This isbecause journal bearings, such as shown in FIG. 1, operate with radialloads, whereas thrust bearings, as shown in FIG. 2, operate with axialloads. However, both types of bearings operate similarly by employinghydrodynamic fluid films, such as air or other fluids, to both providebearing lubricant and cooling.

In the example embodiment of FIG. 2, the thrust bearing 200 includesthree layers, but may include more or fewer layers. A first layer 202comprises multiple arcuate top foils 204 that are spacedcircumferentially relative to one another about a central axis. The topfoils 204 are supported by a second layer 206 having a correspondingnumber of arcuate bump foils 208 arranged circumferentially beneath thetop foils 204. The bump foils 208 are corrugated to provide cushioningand accommodate a cooling airflow through the thrust bearing 200. Athird layer 210 is provided as an annular main plate 212 that supportsthe bump foils 208. The three layers 202, 206, and 210 can be secured toone another, for example, by spot welding. A rotating component 214,such as a thrust plate on an end of a rotating shaft can be positionedadjacent to the top foils 204. The rotating component 214 is typicallyin close proximity to the top foils 204, but for ease of illustration isshown in a partial exploded view with an exaggerated distance betweenthe top foil 204 and the rotating component 214. During operation,moving air generated by action of the rotating component 214 urgespressurized air against the compliant foil structure to create a fluidair layer separating the rotating component 214 and the thrust bearing200. As with the journal bearing 100 of FIG. 1, the surface layer (notshown) can be on the surface of the bearing surface on the radiallyinner surface of top foil 204, or the surface layer can be on theradially outer surface of the rotating component 214, or the surfacelayer can be on the surface of the bearing surface on the radially innersurface of top foil 204 and on the radially outer surface of therotating component 214.

In some embodiments, the above described hydrodynamic bearings can beemployed in an air cycle machine such as those employed on aircraft. Thehydrodynamic bearings provide a long lasting bearing with minimal to norequired maintenance. This is because the bearings employ air as both alubricating fluid and as a cooling fluid, which means that separatelubricating or cooling liquids are not typically required. An exampleembodiment of an air cycle machine is shown in FIG. 3. As shown in FIG.3, an air cycle machine 300 is part of an environmental control systemthat is configured to supply conditioned air, for example, to a cabin ofan aircraft. The air cycle machine 300 is a four-wheel air cyclemachine, with four rotors on a single shaft 304. The four rotors arefixed together and are supported by bearing elements. There are, thus,four bearings configured within the air cycle machine 300 which arearranged along an airflow passage 306, which is represented by the pathof arrows in FIG. 3. The air flow passage 306 provides air as both alubricating fluid for the hydrodynamic bearings and as a cooling airflow to remove heat generated by the bearings during operation.

In the example configuration of FIG. 3, two of the four bearings arethrust bearings and two are journal bearings, as described above. Thethrust bearings are located at the inlet side of the airflow passage306, with the journal bearings located further downstream in the airflowpassage 306. A first thrust bearing 308 is configured as an outboardthrust bearing and a second thrust bearing 310 is configured as aninboard thrust bearing. After the thrust bearings 308 and 310, in thedirection of the airflow passage 306, a first journal bearing 312 isconfigured as a turbine journal bearing and then, toward the outlet ofthe airflow passage 306, a second journal bearing 314 is configured as afan journal bearing. The thrust bearings 308 and 310 are configured tooperate with axial loads, and the journal bearings 312 and 314 areconfigured to operate with radial loads within the engine 302. As anon-limiting example, the air cycle machine 300 may operate at20,000-50,000 RPM. However, other rotational speeds of operation may beused.

While the present disclosure has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present disclosure is not limited to such disclosedembodiments. Rather, the present disclosure can be modified toincorporate any number of variations, alterations, substitutions orequivalent arrangements not heretofore described, but which arecommensurate with the spirit and scope of the present disclosure.Additionally, while various embodiments of the present disclosure havebeen described, it is to be understood that aspects of the presentdisclosure may include only some of the described embodiments.Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

1.-17. (canceled)
 18. A bearing comprising a support, a bump foil overthe support, a top foil over the bump foil, and a surface layer over thebump foil comprising solid lubricant 2D nanoparticles in a matrix, saidnanoparticles having 1 to 20 atoms along a first dimension and beingpresent in the surface layer in a concentration of 35 wt. % to 72 wt. %based on total weight of the surface layer.
 19. The bearing of claim 18,wherein the solid lubricant 2D nanoparticles comprise graphene,hexagonal boron nitride, molybdenum disulfide or combinations thereofgraphene.
 20. The bearing of claim 18, wherein the solid lubricant 2Dnanoparticles have a thickness of 1 to 20 atomic layers and include anx-y planar dimension of 10 nm to 25 μm.